Hybrid and electric vehicle utilize a traction battery to provide power for propulsion and accessory loads. During operation, a state of charge (SOC) of the battery changes as the traction battery is charged and discharged. The SOC may be monitored to ensure that the SOC remains within acceptable limits. Operating the traction battery outside of the acceptable SOC limits may affect battery life. The SOC value may be used to determine when to operate the traction battery in a charging or discharging mode.